Dialysis as a medical therapy for patients with an impaired or lost renal function has been described extensively together with its varied technical aspects in the literature.
For hemodialysis, around 120 to 180 liters of hemodialysis solution are required for one treatment. This is a watery solution, typically of the following composition:
Component Concentration range Typical concentration Na.sup.+ 125-150 mmol/ltr. 128 mmol/ltr. K.sup.+ 0-5 mmol/ltr. 2 mmol/ltr. Ca.sup.+ + 0.3-2.5 mmol/ltr. 1.5 mmol/ltr. Mg.sup.+ + 0-1.5 mmol/ltr. 0.5 mmol/ltr. Cl.sup.- 92-120 mmol/ltr. 110 mmol/ltr. HCO.sub.3.sup.- 30-40 mmol/ltr. 32 mmol/ltr. Acetate 1.5-4 mmol/ltr. 3 mmol/ltr. Glucose 0-3 g/ltr. 1 g/ltr.
The hemodialysis solution is manufactured in a dialysis unit by mixing electrolyte concentrates with pure water. The composition here must meet the physiological requirements as the hemodialysis solution comes into contact with the patient's blood through a semipermeable membrane.
The problems involved in preparing a suitable, physiological composition of hemodialysis solution are presented, for example, in detail in the book "Replacement of renal function by dialysis" (by W. Drukker, F M Parsons, J. F. Maher, Publishers: Martinus Mijhoff Medical Division Den Haag) in the main section "The composition of dialysis fluid" (authors: F. M. Parsons, A. M. Davison).
It is known and is also seen from this publication that the composition of the hemodialysis solution has to be adapted to the specific needs of the individual patient.
As 120 to 180 liters of hemodialysis solution are required for a treatment of four to six hours, it is appropriate to prepare the hemodialysis solution at the place of application.
Dialysis units have been developed where the hemodialysis solution is manufactured continuously or in small partial quantities by means of automatic dosage devices. This is normally done in such a manner that a ready-made fluid concentrate is diluted with pure water in a certain volumetric ratio (the standard ratio being one volume unit of concentrate to 35 parts of the finished solution). Fluid concentrates in a variety of composition versions are available for this method.
The application of the dialysis concentrates at the units is performed in a number of different ways. One standard technique is that of a so-called central supply. Here, a fairly large number of dialysis units of a center are supplied with concentrate via a pipe system from one central location.
One serious disadvantage of central concentrate supply is, however, that it is not possible to have a specific adaptation of the composition to the needs of the individual dialysis patient as only one concentrate type at a time can be distributed via a concentrate supply network.
The use of concentrate canisters at the individual dialysis unit is the most widespread application. The unit is then connected to a supply line through which the pure water (prepared and with controlled quality) is supplied. The concentrate is made available at the dialysis unit in commercial canisters (e.g. 6 or 10 liters) and taken up by the unit through a device led into the canister.
One big advantage of this method is that a particularly suitable concentrate can be selected for the treatment of each individual patient. Such an adaptation, known under the name of "individualization", is generally recognized as being important.
The use of concentrates in canisters represents a substantial strain on the persons working in dialysis wards as the concentrate canisters weight up to 10 kg. The stocking of different concentrates in such large canisters requires a great deal of effort. For a dialysis ward with 20 treatment sites, the typical stock quantity for one week will be on the order of 200 to 300 canisters. Residues of concentrates not fully used up, which remain in the canister after the treatment, should not be used again for a number of reasons. The disposal of these residues, which may well make up to 30 per cent of the actual quantity required, represents a substantial pollution of the environment. The used, empty canisters, normally canisters made of high-quality thermoplastics, cannot be reused for the same purpose according to the state of the art and when taking economic and organizational criteria into account. Returning them into the raw material cycle by means of recycling is, however, not a very economic process, either.
In addition, the hemodialysis solution containing bicarbonate cannot be made from just a single solution concentrate. Concentrates that contain Mg.sup.++ and/or Ca.sup.++ are only stable without bicarbonate, because the presence of bicarbonate precipitation of carbonate to occur.
Bicarbonate dialysis therefore requires the use of at least two separate concentrates, namely a bicarbonate concentrate, usually in the form of a pure sodium bicarbonate solution, and a concentrate of the other components of the solution, this latter concentrate normally bearing the name "acid bicarbonate hemodialysis concentrate". The hemodialysis units intended for bicarbonate dialysis must be equipped with two separate dosage proportion devices for these two concentrates.
The risk of precipitation of carbonates only occurs with this method after the components have been mixed. However, this is of only minor significance in hemodialysis as the length of time the mixed hemodialysis solution spends in the line system of the dialysis unit, including the dialyzer, is only on the order of one minute.
Another problem in bicarbonate dialysis is that the commercial bicarbonate solution is not autosterile. The bicarbonate concentrate must therefore be produced in a sterile form with increased care and be stored in sterile form in suitable containers until use.
The fluid concentrates described above contain up to 80% water and are therefore of great disadvantage from a logistical point of view.
In addition to the fluid concentrates, there is the possibility of manufacturing the concentrates on site from the raw salts. The salts must then be dissolved in pure water prior to the treatment. Their manufacture requires great care and is very time consuming.
An alternative is provided by granulates which consist exclusively of the substances required for dialysis. For example, bicarbonate granulates are already known as a first, base concentrate, with the rest of the total solution components consisting of the electrolytes (Mg.sup.2+, Ca.sup.2+, K.sup.+ Na.sup.+) and a physiologically compatible acid being comprised in a second concentrate. It is also already known to take the sodium chloride portion out of the acid electrolyte portion and to dispense it as a third concentrate for an individual patient treatment. This has already been described in EP 0 613 688.
For example, it is also already known from EP 0 602 014 A1 to make the electrolyte portions available in granulate form. Here, it has already been described that the desired acetic acid quantity is added to this granulate of the electrolytes. However, according to the state of the art, there is the risk that the granulates manufactured there lose their free-flowing capability due to the absorption of the acetic acid.